Seats such as vehicle seats and sofas placed in a house have a seat pad and a skin material. The seat pad is formed of a foamed synthetic resin such as a flexible polyurethane foam or a semirigid polyurethane foam. The skin material is disposed on the surface of the seat pad.
Nowadays, in some case, an airbag device is installed in a vehicle seat so as to inflate an airbag between the occupant and the side surface of a vehicle cabin when, for example, a vehicle is involved in a side crash or a vehicle is overturned. In this case, a through hole or a recess in which the airbag device is housed may be formed in a seat pad. In addition to the above-described case, a variety of hole-like portions may be formed in the seat pad. Examples of the hole-like portions include a recess with which a seat frame is engaged and through holes into which support legs of a head rest, speakers, and so forth are inserted.
In order to form a seat pad having a hole-like portion with a mold, a projection for forming the hole-like portion is provided on the inner surface of the mold. The outer shape of the projection is the same as the inner shape of the hole-like portion. When a seat pad main body is formed by foaming the material of a foamed synthetic resin in the mold, the hole-like portion is formed at a portion where the projection was present after the seat pad has been demolded.
FIG. 15a is a longitudinal sectional view illustrating an outline of a typical related-art mold for forming a seat pad having a through hole. FIG. 15b is a longitudinal sectional view of the seat pad formed with this mold. As illustrated in FIG. 15a, a mold 110 includes an upper die 111 and a lower die 112 (and a core according to need). A seat pad 100 is formed by supplying a raw material of a foamed material such as urethane into the lower die 112, clamping together the upper and lower dies 111 and 112, and foaming the raw material. In general, in the mold 110, the seat pad 100 is formed in a position in which a surface thereof opposing an occupant seated in the seat facing downward. In this related-art example, a reinforcing member 101 is integrally formed with a surface of the seat pad 100 opposite to the surface opposing an occupant seated in the seat (hereafter, this opposite surface may be referred to as a rear surface).
In this related-art example, a projection 113 for forming a hole projects from a cavity bottom surface of the lower die 112. By using the projection 113, a hole 102 is formed from the surface opposing an occupant seated in the seat toward the rear surface in the seat pad 100. That is, the hole 102 is formed at a portion where the projection 113 was present during foam molding.
I a state in which the upper and lower dies 111 and 112 are clamped together, a tip end surface (upper end surface) of the projection 113 is slightly separated from a cavity top surface of the upper die 111. The separation is intended to ensure that the upper and lower dies 111 and 112 are in tight contact with each other at a surface where the upper and lower dies 111 and 112 are in contact with each other. The separation is also intended to prevent air from accumulating around the hole 102 during foam molding. That is, by separating the tip end surface of the projection 113 from the cavity top surface of the upper die 111 as described above, even when, during foam molding, air remains in a corner portion where an outer peripheral surface of the projection 113 and the cavity top surface of the upper die 111 intersect each other, the air together with foamed resin enters the gap between the projection 113 and the upper die 111. Accordingly, in the seat pad 100 formed with this mold 110 by foam molding, a burr portion 103 that closes the hole 102 is formed as illustrated in FIG. 15b because the foamed resin enters the gap between the projection 113 and the upper die 111 during foam molding. Thus, the burr portion 103 needs to be removed after the seat pad 100 is demolded.
Japanese Utility Model Publication S55-166622A describes a mold for forming a seat pad. With this mold, removal of the burr portion 103 can be facilitated. FIG. 16a is a longitudinal sectional view of the mold described in the above-described document. FIG. 16b is a longitudinal sectional view of a seat pad formed with this mold. As illustrated in FIG. 16a, in this mold 110′, a recess 114 recessed toward the outside of the mold 110′ is provided in a region of the cavity top surface of the upper die 111, the region opposing the tip end surface of the projection 113. During foam molding, the foamed resin enters the recess 114 through the gap between the tip end surface of the projection 113 and the cavity top surface of the upper die 111. Accordingly, in a seat pad 100′ formed with this mold 110′, a burr block 104 is formed of the foamed resin having entered the recess 114 so as to protrude from the outer surface of the seat pad 100′ as illustrated in FIG. 16b. Thus, when removing the burr portion 103 that closes the hole 102 after the seat pad 100′ has been demolded, the burr portion 103 can be easily removed by picking up the burr block 104.
Japanese Patent Publication 2008-154839A describes a groove (not shown) provided in the surface of the seat pad 100. The groove indicates an area (contour) of the hole 102. In order to remove the burr portion 103 that closes the hole 102 with a cutting means (not shown) such as a cutter, the groove facilitates the removal of the burr portion 103. Japanese Unexamined Patent Application Publication No. 2008-154839 also describes that a cutting recess (not shown) is provided inside this area so as to be in contact with the groove. In order to remove the burr portion 103, the cutting means is inserted into the cutting recess, and the foam is cut from this position along the groove. This allows the burr portion 103 to be comparatively easily removed. According to the above-described document, a housing portion, in which a side airbag device is housed, is defined by the hole 102 after the burr portion 103 has been removed.
In the case where the hole 102 is a non-through hole, in a state in which the mold 110 is clamped, a gap having a predetermined size is formed between the tip end surface of the projection 113 and the cavity top surface of the upper die 111. When the foamed resin enters the gap between the projection 113 and the upper die 111 during foam molding, a bottom portion of a non-through hole 102 is formed.